Just a few months ago, the Prime Minister rightly rejected the toxic EU proposal to interfere with the UK single market, saying “no British Prime Minister could ever sign up to it”. Understandably so, as such a proposal would fundamentally damage our constitutional integrity. A deal which contains such proposals, which is what is being reported as I write this, means she has failed even her own test.

Be not mistaken, fracturing our United Kingdom, constitutionally or economically, is bad for all of us across this country. The constitutional significance of breaking the UK single market cannot be over-estimated. Our Union would never be the same again, diminished to the detriment of our national...